The invention relates to a multipart cooled piston for a combustion engine with a piston upper part of forged steel comprising a combustion bowl and a ring wall with ring belt, and with a piston lower part comprising a piston skirt, pin bosses for receiving the piston pin connecting the piston to the connecting rod, and pin boss supports connected to the piston skirt, and to a method for manufacture of a piston of this type.
A multipart cooled piston for a combustion engine is known from JP 61175255 A. This piston has at the level of the ring belt of the piston a number of ribs, between which is arranged a thermally insulating plate for minimization of the heat transfer from the combustion chamber bowl to the ring belt.
From WO 00/77379 A1, a further piston for a combustion engine is known which has a wall section with several transverse walls made of thin metal sheet and radially arranged in order to improve the heat dissipation in the cooling channel.
The above designs are not suitable for improvement of the piston in respect of its stability for high ignition pressures and temperatures as encountered in modern diesel engines.
The object underlying the present invention is therefore to provide a piston concept for a multipart cooled piston with which inexpensive manufacture is assured and with which piston deformation due to the effects of high gas pressures and temperatures can be effectively countered.
The solution to the problem is set forth in the independent claims.
In accordance with the invention, a method is indicated for manufacture of a multipart cooled piston in which the piston upper part is provided, by forging of a blank, with supporting ribs in the cooling channel that each form sections of an all-round ring rib radially to the longitudinal piston axis. The piston upper part furthermore comprises a combustion bowl and a ring wall with ring belt. Following this, the blank forged in this way is prepared for connection by machining of the connecting surface.
A forged piston lower part comprising pin bosses, pin boss support and piston skirt is provided with an annular and all-round carrier rib connecting the pin boss supports, and is likewise prepared for connection after the forging process. The subsequent joining or connection of the ring rib of the piston upper part to the carrier rib of the piston lower part is achieved by means of a welding or soldering process. Then the piston blank connected in this way is finish-machined into a piston usable for an engine.
Advantageously, the supporting ribs can be made or arranged radially symmetrically and/or non-symmetrically spread over the circumference of the cooling channel, for example by a larger number thereof in the major/minor thrust direction of the piston. With a piston manufactured in this way, the cooling channel can be formed closer towards the piston crown or combustion bowl and nevertheless has excellent form stability. In addition, the arrangement of the supporting ribs effects a kind of chamber formation inside the cooling channel, i.e. creates shaker areas, whereby a prolongation of the dwell time of the cooling oil is achieved and hence an improved heat dissipation of the piston areas to be cooled.
With the solution in accordance with the invention, piston upper parts of heat-resistant steel and piston lower parts comprising forged AFP steel can be manufactured and connected in a particularly simple and inexpensive way.
Advantageous embodiments are the subject-matter of sub-claims.